Manufacture of safety razor blades



April 1936. H. L. CLAISSE 2,038,415

MANUFACTURE OF- SAFETY RAZOR BLADES" Filed Apri1.21, 1933 Fig. 5. 4 7

Patented Apr. 21, 1936 MANUFACTURE OF SAFETY RAZOR BLADES HerbertLefevre Claisse, London, England, as- "signor to Gillette Safety RazorCompany, Boston, Mass., a corporation of Delaware Application April 21,1933, Serial No. 667,208 In Great Britain May 13, 1932 9 Claims. (Cl.148-10) The present invention relates to the manufacture of. safetyrazor blades of the thin flexible type having a continuous-slot ofsubstantial length, e. g., extending substantially over the whole lengthof the cutting edge of the blade, and having end portions which areintended to be bent transversely and maintained in a position ofcurvature during use, and whose medial parts are substantially softerthan the cutting edges.

In one aspect the present invention consists in improvements upon theinvention the subject of the copending applicationof Otto Roth, SerialNo. 666,641, filed April 18, 1933, which issued as U. S. Patent No.1,989,886, on Feb. 5, 1935.

In another aspect the invention comprises improvements having generalapplication to the production of thin flexible safety razor blades ofdifferential hardness whereby certain portions of the blade are renderedsubstantially softer than the cutting edges.

With known methods of producing such blades it is difficult to obtainthe desirable degree of hardness of the cutting edges, if the medialarea is to be sufficiently soft to permit the blade to flex without riskof. fracture. Moreover such prior methods are very liable to producedistortion of blades so as to render it commercially impracticable toproduce finished blades with an even cutting edge by grinding in thestrip.

The object of the present invention is to facilitate obtainingdifferential hardening, and to enable the manufacturer to obtain moreeasily such differing conditions of edge and medial hardness as he maydesire.

What are the optimum, conditions is to some extent a. matter of opinion.It has been found that a blade with an edge hardness of about 850 on theVickers Hardness Testing Machine and a hardness of 100 or less near themedial projections gives good results in practice, but it should beobserved that with these blades it is a matter of great difliculty toobtain the exact degree of hardness represented by these figures foreach and every blade. v p

To this end use is made of the process disclosed in the aforesaidco-pending application No. 666, 641, this process being characterized bythe employment of an electric current in connection with a hardenedblade of such configuration and proportion that there is a substantialdifference between the density of the current flow in difierent portionsof the blade, the greatest density of. such flow being in the endportions where the metal should beof the lowest degree of hardness, andleast density at and near the cutting edge, the heating effect at eachpoint being proportional to I R, where I is the density of the currentflow at such point and R the resistance.

To obtain this differential density the current,

is applied to a blade having a medial slot of substantial length, andend portions so shaped that the breadth of metal available for thepassage of the current through such end portions is substantially lessthan that so available in the medial portion of the blade, e. g., in thecutting edge carrying portions thereof, whereby the density of thecurrent flow in such end portions is increased beyond that near thecutting edges.

The length of the slot, its terminal form and the restriction of thebreadth of metal in the end portions has an important effect inproducing the differential density of the current flow through theblade.

With a slot of substantially even breadth and the current entering andleaving at the ends of the blade the density of. the current flow nearthe medial line of the blade will also tend to be somewhat greater thanat or near the cutting edge, since the path from electrode to electrodeis less near such medial line.

The process is applicable to blades of known shape, e. g., such as thoseshown in U. S. Letters Patent Nos. 1,869,327, 1,850,902 and 1,858,316since the end portions of such blades possess the requisite qualitiesabove described.

The present invention is particularly suited for continuous operation incases where the blades are hardened, tempered and sharpened in thestrip, which after the punching operation consists as shown in Fig. 2.of the drawing hereinafter referred to, of a series of blade blanks (a)havin continuous slots (b) the blade blanks being joined end to end bynarrower portions or necks (c) which are finally severed to leave equalportions thereof on adjacent blades.

The method is applicable both to cases where blades are hardened and/ortempered and/or sharpened in the strip, and where individual blades arehardened and/or tempered and/or sharpened separately.

In so far as the present invention consists in improvements upon theinvention the subject of Roth's co-pending application Serial No, 666,-641, filed April 18, 1933, the present process is characterized by firsthardening a blade of the kind referred to and-then tempering the bladeby any known or approved methods to a general blade in an electriccircuit so that the current enters and leaves at the narrower endportions.

Thus according to the present invention intermediate methods may be usedin which various degrees of softening are employed prior to theelectrical treatment.

sharpening the blades while still on strip form. Owing to the fact that,the end portions of the blade at which the current enters and leaves areof less cross sectional area than the main portion of the blade thecurrent density will be substantially greater at the end areas thanalong the main portion of the blade, whereby such a differentialtempering is obtained between the end areas and the main portion of theblade as will givethe blade the characteristics hereinbefore referredto.

In order that the invention may be the more readily understood referenceis hereinafter made to the accompanying drawing in which:--

Fig. 1 is a diagrammatic view of one form of apparatus for carrying outthe present process, and

Fig. 2 shows part of a strip of blade blanks adapted to be treated bythe process.

Fig. 3 shows diagrammatically a variant way of applying the current.

Fig. 4 shows part of a strip of blade blanks of a modified form, and

Fig. 5 shows a part of a further modified form of strip.

Referring to Fig. 1 of the accompanying drawing, the strip of blades,after being hardened and tempered by passing through a hardeningapparatus I and then subsequently through a general tempering apparatus2, is caused to bridge a gap in an electric circuit, so that with ablade with a longitudinal slot the current will divide into two partsbetween the successive necks.

A general tempering apparatus 2 which serves well comprises a tube inwhich is a coil 3 in a circuit 4 which is connected to the electricmains 5 by a double pole switch 6. In the circuit 4 is an ammeter l anda variable resistance 8. An inert gas may be passed through the tube toavoid oxidation. I2 is a pyrometer.

The strip leaves this apparatus 2 with an all over even tempersubstantially at or slightly exceeding working edge hardness.

The strip'now passes to the electrical treatment apparatus comprisingspaced apart pairs of contact blocks 9, 9a; and I0, Ma. The blocks.

are held to the strip by light spring pressure so that they formyielding clamp contacts. The blocks 9, 9a and I0, Illa. are watercooled, apart of the water cooling system being indicated by H. Thewater in the blocks 9, 9a is preferably insulated from the contacts.This water cooling of the blocks prevents heat from the centre of thestrip-spreading over the blocks and thus being transmitted to the edgeof the strip.

The blocks 9, 9a and I0, Illa are units in an open circuit Ha, havingtherein a variable resistance I2a, a single pole switch 13, an ammeterI4, and the secondary winding [5 of a transformer, the primary winding16 being connected to the mains by a double pole switch H. I8 is avoltmeter connected across the circuit II. The circuit-I I is closed bythat part of the strip which for the time being bridges the gap betweenthe contact blocks 9, 9a and I0, Illa.

To avoid or minimize oxidation during the differential heating it isconvenient to arrange forthe part of the strip under treatment to besurrounded by an inert gas.

A working example of voltage and amperage for a strip in which theblades are proportioned as shown each blade being about 43 mm. long is 4volts. 60 amps, with 12 blades between the contacts, the speed of stripgoing through being 145 blades a minute.

The strength of the current is so chosen with respect to the rate offeed of the strip, and the distance the contacts are spaced apart, thatin the time that the blade is subject to the heating effect of thecurrent the necks are softened the desired amount, without reducing orsubstantially reducing the edge hardness of the strip. In other words,the hardening and tempering of the blades may be carried out with alldesired accuracy in separate operations and then the endsoftenirigoperation may be separately carried out on the previously temperedblades without being complicated by any considerations affecting thetempering of the cutting edge carrying portions of the blades.

Figure 3 shows, applied to a single blade, an other way of carrying outthe present process and applicable also to the process according toRoths co-pending application Serial No. 666,641, filed April 18, 1933,in which the current enters and leaves by way of the cutting edges. Inthis method long contacts can be employed for example extendingsubstantially over the length of the cutting edges.

Fig. 4 illustrates a modified form of blade strip in which the end areasof the blade blanks are perforated with slits or slots e to facilitatethe localization of the high current density to the medial end portionsof the blades both according to the present process and according tothat the subject of Roths co-pending application No. 666,641, filedApril 18, 1933.

By the present invention the following factors are under themanufacturers control; the hardness of the blade before treatment, thestrength of the current, the time during which it is applied, the widthof the end portions through which the current enters and leaves theminimum breadth of metal available for the path of the current near theends compared to that of other portions of the blade, and by experimentor calculation these features can be so varied as to obtain a greatvariety of differences of temper.

Further, where the current is applied to a strip containing a number ofblades, the differentiation of current density may be increased by nick-I ing or the like, so that the breadth of the parts by which the currententers or through which it leaves is decreased. Nicks d at the necksbetween the blades are shown in Fig. 2.

In some cases it may be advantageous both in the case of strips and alsoof single blades to have nicks or slots parallel to the medial line tofurther control the current flow. In some cases curved or inclined nicksor slots may be used for this purpose.

The present invention also embraces a variant method wherein instead ofjoining the blades end-to-end in strip form, they are joined side-tosideas shown in Fig. 5 so that the medial longitudinal' slots in the bladeslie transverse to the direction of length of the strip and parallel toeach other. The electric current then enters and leaves by way of theblade portions, which are to contain the cutting edges, at each side ofthe longitudinal slot as in the arrangement according to Fig. 3 andtravels in a general direction transverse to the slots b. The bladeblanks are subsequently severed along the lines 1 and sharpened.

Apart from the specific advantages above described the use of theelectric current avoids many of the difficulties attached to othermethods of tempering.

What I claim is:-

1. A process of producing thin flexible razor blades with high edgehardness and relatively softer medial end areas, which consists inapplying an electric current to a hardened blade having a mediallongitudinal slot of substantial length and having the combinedsectional area of the portions at each end of the slot substantiallyless than the longitudinalsectional area through the cutting-edgecontaining portions of the blade at opposite sides of the slot, andcausing the current to flow in'a general direction transverse to saidslots and from one cutting-edge containing portion to the other throughsuch end portions so that the density of the current is substantiallygreater over the medial end portions than at the cutting edges.

2. Process for the production of thin flexible razor blades with a highedge hardness and relatively softer medial end areas, comprisingsubjecting a plurality of blades which are provided with a longitudinalslot of substantial length to hardening and general tempering operationsto produce in the edge substantially the hardness required for shavingpurposes, and then applying an electric current to such blades, the saidblades being connected longitudinally in strip form by necks ofsubstantially less cross-sectional area than the main portion of theblade so that the density of the current will be substantially greaterover the medial portions of the blades than at or near the cuttingedges.

'3. Process for the production of thin flexible razor blades with highedge hardness and relatively softer medial end areas, comprisingapplying an electric current to a plurality of hardened blades which areprovided with a longitudinal slot of substantial length and areconnected longitudinally in strip form, the crosssectional' area of thestrip between the slots being considerably less than that of the mainpart of the strip so that the density of the current will besubstantially greater over the medial end portions of the blade than ator near the cutting edges, said strip having longitudinally extendingnicks or slots at the junctions of adjacent blades to control thecurrent flow at said junctions. a

4. Process for the production of thin flexible razor blades with highedge hardness and relatively softer medial end areas, which consists inapplying an electric current to a plurality of blades havinga mediallongitudinal slot of substantial length, said blades being joined instrip form with the slots lying transversely of the strip, the combinedcross-sectional area of the portions of the strip at the ends of eachslot being sub.- stantially less than'that of the portions between theslots so that the density of the current is substantially greater in theportions at the ends of the slots than in the portions between theslots,,'

and then severing the blades between the slots and sharpening the edgesthus produced to form cutting edges. I

5. The-step in the production of thin flexible razor blades with highedge hardness and relatively softer medial end areas, which consists inapplying an electric current to a plurality of blades having a mediallongitudinal slot of substantial length, said blades being joined instrip form with the slots lying parallel to each other, the combinedcross-sectional area of the portions of the strip at the ends of eachslot being substantially less than that of the portions between theslots so that the density of the current is substantially greater in theportions at the ends of the slots than in the portions between theslots.

6. Process for the production of thin flexible blades with high edgehardness and relatively soft medial end areas, which comprisessubjecting a blade having a medial slot of substantial length tohardening and general tempering operations and subsequentlyend-softening the tempered blade, while maintaining the edge hardnesspreviously imparted thereto, by applying an electric current to theblade, the cross-sectional area of each end portion of said blade beingsubstantially less than that of the main portion so that the intensityof the current is substantially greater over the medial end portionsthan at or near its cutting edges. 7

'7. A process for producing thin flexible razor blades with high edgehardness and relatively softer medial end areas, which comprisessubjecting a blade having a medial slot of substantial length tohardening and general tempering op-' erations to impart to the edgesubstantially the hardness required for shaving purposes, and thenend-softening the tempered blade by applying an electric current to suchblade, while maintaining the edge temper previously imparted to theblade, the sectional areas of the material available for the passage ofthe current through the end portions of the blade being substantiallyless than that available for the passage of the current through the mainportion so that the density of the current is substantially greater overthe medial end portions than at or near the cutting edges.

8. Process for the production of thin flexible blades with high edgehardness and relatively softer medial end areas, which comprisessubjecting a blade having a medial slot of substantial length tohardening and general tempering operations to produce the hardness ofthe edge that is required for shaving purposes, and subsequentlyend-softening the. blade, while maintaining the edge temper previouslyimparted thereto, by applying an electric current to such blade, thecross-sectional area of each end portion of the blade, beingsubstantially less than the combined cross-sectional area of theedgebearing portions, so that the density of the current issubstantially greater over each medial end portion than at or near thecutting edges.

9. A process of producing thin flexible razor blades in strip form withhigh edge hardness and relatively softer end areas, which consistsin-slotting the blade blanks in a strip to define separatededge-carrying portions, perforating the end areas with spaced open-endedslits to reduce locally their cross-sectional area, hardening the stripand then causing an electric current to flow through the strip ofintensity sufiicient to reduce the hardness of said perforated end areasmore than the edge-carrying portions 01. the

